This invention relates to spread-spectrum communications, and more particularly to a wireless distributed network for reducing power and power variations, when transmitting packets having spread-spectrum modulation.
As the data rate increases, the power transmitted by a cellular xe2x80x9ctelephonexe2x80x9d and by the cellular base station (BS) must also increase to ensure a low probability of error. As illustratively shown in FIG. 1, a star network, as is presently used for cellular networks, is used to communicate data between a central office 50 and a plurality of remote stations (RS). A plurality of base stations 20, 30, 40, communicate directly with the central office 50. A first base station 20 communicates data between a first plurality of remote stations 21, 22, 23, 24. A second base station 30 communicates data between a second plurality of remote stations 31, 32, 33, 34, 35, 36. A third base station 40 communicates data between a third plurality of remote stations 41, 42, 43, 44, 45.
In the star network of FIG. 1, data, in general, are not communicated directly between base stations, but through the central office 50. The routing of data is a fixed communication path, from a remote station through a base station to the central office, and vice versa. Data generally are not routed, with dynamically changing paths, between remote stations which communicate with a base station, and data are not routed between remote stations directly through base stations, without passing through the central office 50. Also, data are not routed to the central office 50, using communications paths which dynamically vary between base stations, depending upon availability.
The power transmitted by the base station and the remote stations, and the ability to properly control the power, are problems which are growing in importance with the start of third generation (3G) wireless systems, which stresses data transmission which requires low error rates and Internet access.
Previously, a user could transmit data at the rate of 9.6 kilobit per second (Kb/s). Now, with 3G wireless systems, this rate is increasing to 384 kb/s and higher. For the increased data rates, the power must increase by a factor of 40 or more to ensure no degradation of performance.
A proposed solution to this problem is to install additional base stations, or towers. This is a very costly solution since some base stations will be overloaded with traffic and other base stations underutilized. This solution, however, certainly will reduce the power transmitted. Users who are distant from the base station still will be required to transmit significantly larger power than users located near the base station, to alleviate the near-far power problem. This very significant difference in distance and therefore in transmitted power, requires very accurate power control, which is a limiting feature in the current, standardized, 3G system. For example, consider acquisition: One limitation is effective packet size; that is, it takes significant time for the base station to help the user adjust its transmit power to the correct level. As more time is required, the packet will, in effect, increase in length, using time which could be allocated for data transmission or the transmission of additional data packets. This xe2x80x9cramp upxe2x80x9d time could exceed the duration of the data portion of the packet itself. As another example, during power control adjustment, a user transmitting with too much power can increase the error rate of a user transmitting at the proper power level.
The present base station multi-access scheme currently in use is not a preferred system approach.
A general object of the invention is to increase capacity of data from remote stations to a central office.
Another object of the invention is to reduce power levels and power level variations required for transmitting from remote stations and from the base stations.
An additional object of the invention is a more flexible network, which dynamically adapts to changing data requirements between remote stations and a central office.
According to the present invention, as embodied and broadly described herein, a distributed network, spread-spectrum system is provided, comprising a plurality of remote stations and a plurality of nodes. The plurality of nodes forms the distributed network. The distributed network plus the plurality of remote stations form the distributed system. In the plurality of nodes, one or more nodes are hub nodes, which connect to a central telephone office. The plurality of nodes covers a geographic area. Each node covers a micro-cell having a radius, which, typically, is less than one mile. Each node includes a plurality of spread-spectrum transceivers, or, equivalently, a plurality of spread-spectrum transmitters and a plurality of spread-spectrum receivers. Each node also includes a store-and-forward subsystem, and a flow-control subsystem, at least one node transmitter, and more typically a plurality of node transmitters, and at least one node receiver and more typically a plurality of node receivers.
Transmission between the remote station and a node is through the use of CDMA modulation, although any other modulation technique may be employed. Transmitting between nodes may be by cable, fiber optic cable, or microwave link, using any of a variety of modulation techniques. Steerable antennas may be employed. Such modulation and communications channels are well-known in the art.
Each node""s spread-spectrum transceiver communicates, using packets having spread-spectrum modulation, over radio waves, with a plurality of remote stations. Each packet has a source address and a destination address, and may contain other information such as flow-control information, forward error correction, and message data. The store-and-forward subsystem stores and forwards one or more packets to and/or from the remote station. The store-and-forward subsystem stores and forwards the one or more packets to and from another node in the plurality of nodes.
A node transmitter communicates with a node receiver located at a different node from the transmitting node.
The flow-control subsystem in the distributed network controls the store-and-forward subsystem, to store each packet arriving at the spread-spectrum transceiver. The flow-control subsystem communicates traffic information between each of the nodes in the plurality of nodes. The traffic information typically includes traffic density at each of the nodes and node-memory availability. Using the traffic information, and in response to a packet having the destination address to the hub node, the flow-control subsystem routes the packet through appropriate nodes to the hub node or, in the case of a xe2x80x9clocal callxe2x80x9d, to the remote user directly. A xe2x80x9clocal callxe2x80x9d is defined as a call between remote stations located within (i.e., accessing) the same distributed network. For the local call, the central office connection is not required.
Based on the traffic at each node, and each packet having a destination address to a remote station, the flow-control subsystem transmits the packet from a central office to an appropriate hub node to an appropriate node, and routes the packet to the next recipient node. Each packet in a message may traverse a different route. In response to a plurality of packets having voice data, the flow-control subsystem routes the plurality of packets through the same path in the plurality of nodes to ensure that the plurality of packets arrive sequentially. The flow control procedure balances the activity in each node relative to other nodes in the distributed network.
When an information packet(s) arrives from a remote station, the node routes the packet(s) to an appropriate second recipient node on the way to an intended hub node and central office, toward the destination address.
Additional objects and advantages of the invention are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.